There is disclosed in the art a complementary metal oxide semiconductor (CMOS) operational amplifier circuit having a differential input circuit part and a folded cascode circuit part.
The differential input circuit part includes a p-type metal oxide semiconductor (p-type MOS) transistor differential pair and an n-type metal oxide semiconductor (n-type MOS) transistor differential pair that have common positive and negative input terminals, a first constant current circuit configured to supply an operating current to the two transistor differential pairs, and a current switching circuit configured to switch the supply of current of the first constant current circuit to the two transistor differential pairs.
The folded cascode circuit part includes a cascode current mirror circuit, second and third constant current circuits, each of which is connected to the cascode current mirror circuit in series, and a bias voltage source configured to apply a bias voltage to the cascode current mirror circuit.
The bias voltage source raises the bias voltage while the operating current flows in the n-type MOS transistor differential pair.